While I appreciate that the NH October circulation might indeed give an indication of what the dominant winter circulation might be, I find the statistics of the OPI 'averaging' really odd.
E.g. the 31st October OPI (which is seemingly the overall October OPI) depends on the 22nd October OPI... which in turn depends on a simulated 0-9 day forecast. So my (surely flawed?) interpretation gives a final 2014 OPI that depends on forecast approximations.
It's possible that a forecast contains hidden info that's lost with the actual evolution, but it seems odd.
Also, surely the 1980s data points weren't calculated using 10 day forecasts... modelling at 10+ days was really poor in those days, so that graph with nice correlations must use different calculations in different decades.
But then that does away with any reason for using 10 day forecasts now.
If last century's data points used reanalysis data, then strictly speaking to be consistent we need to redo the calculations after the 31st October using actual weather data, not forecast data. Or perhaps they do this anyway, I don't know.
And why not use 3rd October - 2nd November: does the theory just collapse then or what?
(A confused Mrs Dee)
